KR20000022369A - Catalyst for dehydrogenation of cyclohexanol, process for the preparation of said catalyst and use thereof - Google Patents

Abstract

PURPOSE: The invention relates to a catalyst comprising alpha-aluminum oxide as the support material and copper as the active constituent. CONSTITUTION: The BET surface of the aluminum oxide being not lower than 30 m<2>/g.It also relates to a process for preparing the catalyst according to the invention, and the use thereof in dehydrogenation of cyclohexanol to form cyclohexanone, and also to the use of alpha-aluminum oxide, the BET surface of the aluminum oxide being not lower than 30 m<2>/g, to prepare a catalyst.

Description

Dehydrogenation catalyst of cyclohexanol, preparation method and use thereof

The present invention relates to an improved α-alumina phase copper catalyst having a BET surface area (measured according to DIN 66131) of at least 30 m 2 / g.

The invention also relates to a process for preparing the catalyst of the invention and its use in the dehydrogenation of cyclohexanol to cyclohexanone, and to the preparation of the catalyst, a BET surface area (measured according to DIN 66131) of at least 30 m 2 / g It relates to the use of alumina.

Cyclohexanone is an important intermediate for nylon-6 and nylon-6,6 and is mass produced industrially by the catalytic dehydrogenation of cyclohexanol. There are two catalytic dehydrogenation methods of cyclohexanol. The high temperature method is carried out at 320 to 420 ° C and the low temperature method at 220 to 260 ° C.

High temperature dehydrogenation has the disadvantage of low cyclohexanol selectivity, since high dimerization occurs at high temperatures such as dehydration of cyclohexanol to cyclohexene or formation of cyclohexanylcyclohexanone. By-products require extensive finishing and reduce the economics of the process.

Low temperature dehydrogenation of cyclohexanol is especially catalyzed using copper based catalysts. These catalysts make it possible to provide higher cyclohexanone selectivity by lowering the reaction temperature to about 240-280 ° C. However, since the equilibrium changes at relatively low temperatures, the conversion rate is generally not very high.

One class of these low temperature catalysts includes compositions of copper and ceramic carriers, which may be SiO ₂ or Al ₂ O ₃ , or mixtures thereof. The copper content of these catalysts can be up to 50% by weight. These catalysts may further comprise small amounts of alkali metals as cocatalysts.

For example, for non-oxidative dehydrogenation of cyclohexanol, GB-A 1081491 is Cu / Al ₂ O ₃ , SU-A 465217 is Cu / Li / SiO ₂ , and 522853 is Cu / K. / Al ₂ O ₃ is disclosed. The present copper catalyst is generally prepared by applying the active copper component to a previously prepared carrier or by coprecipitating the catalyst components, either by precipitation of the copper salt or by impregnation with a suitable copper salt solution. Another way to make a copper catalyst is to dry mix the components and then calcinate the mixture.

Reductive precipitating or electroless coppering of copper on a carrier using a reducing agent in the presence of a complexing agent for the production of a copper catalyst for the non-oxidative dehydrogenation of cyclohexanol has been described by Chang et al. Appl. Catal. A 103 (1994) 233-42). Carriers used include α-Al ₂ O ₃ with a surface area of 22.6 m 2 / g. According to the chapter, the selectivity is influenced by the acidity of the carrier in that an acidic carrier such as Al ₂ O ₃ or SiO ₂ will catalyze side reactions such as dehydration or dimerization to cyclohexene. It is also possible to reduce the acidity by adding alkali metal or alkaline earth metal ions (see, eg, Appl. Cat. A: General Vol. 83, No. 2 (1992), 201-11), but this measure also provides activity Will reduce. Thus, the advantage of higher activity in the case of copper catalysts over high temperature catalysts is lost to some extent by alkali metal or alkaline earth metal doping.

However, the catalysts described in Appl. Catal. A 103 (1994) 233-42 are unsuitable for industrial use because they are powders. Pressing into shaped articles such as tablets is difficult due to inferior tablettability. In addition, the low hardness of the resulting molded article results in low wear resistance in the reactor, which increases the pressure drop in the course of the reaction. Therefore, it is generally not possible to use industrially on a real scale.

Another disadvantage of using α-Al ₂ O ₃ as the carrier material is low interaction with the active copper component. This low interaction causes the active ingredients to aggregate rapidly, resulting in a loss of catalytically active surface area resulting in reduced activity. Nevertheless, the reactor temperature must be raised during the dehydrogenation process in order to achieve high conversion, but this will further facilitate the flocculation of the catalyst and subsequent deactivation of the catalyst.

It is an object of the present invention to provide a catalyst which does not have the above mentioned disadvantages. More particularly, the catalyst should have a long operating life and hydrogenate cyclohexanol to cyclohexanone with high yield and high selectivity at relatively low reaction temperatures. Likewise a constant readjustment of the reaction temperature should not be required. In addition, the catalyst should be able to be easily processed into shaped articles, in particular tablets, strands, cyclics and cylinders, and should also be usable in such forms because of their good hardness and wear resistance.

The inventors have finally found that this object is achieved by an improved α-alumina phase copper catalyst having a BET surface area (measured according to DIN 66131) of at least 30 m 2 / g.

The invention also relates to a process for preparing the catalyst of the invention, the use thereof in the dehydrogenation of cyclohexanol to cyclohexanone and a BET surface area (measured according to DIN 66131) of α for at least 30 m 2 / g Provides the use of alumina

The catalyst of the present invention is prepared by applying the active copper component onto an α-Al ₂ O ₃ carrier having a BET surface area of at least 30 m 2 / g or more in a conventional manner such as impregnation, precipitation, dry mixing or electroless copperation.

The BET surface area of α-Al ₂ O ₃ which is preferably used is 50 to 300 m 2 / g, particularly preferably 100 to 250 m 2 / g. Such high BET values of α-Al ₂ O ₃ are commercially available (eg from Alcoa).

Impregnation generally involves saturating the carrier with an aqueous solution of a copper salt, preferably copper nitrate, sulfate, acetate or chloride, drying and then calcining the impregnated carrier.

Precipitation usually involves mixing an aqueous solution of a copper salt (see above) with a precipitant to form a slightly soluble copper compound in the presence of a carrier. Sodium carbonate is preferred to precipitate copper. Thereafter it is dried and calcined in a conventional manner.

Dry mixing generally involves mixing the carrier with the desired copper salt and then calcining.

In another preferred embodiment, the catalyst is prepared by electroless deposition (copperation) in the presence of high BET values of α-alumina as used herein (see also Appl. Catal. A 103 (1994) 233-242. Reference). For this purpose, the carrier is generally first seeded with a noble metal such as platinum, rhodium, iridium, gold or palladium, preferably palladium, to form a crystallization-initiating center. The copper complex is then treated with a reducing agent so that copper is deposited on the carrier.

In order to prevent premature precipitation of copper at the generally high pH required, it is desirable to add strong complexing agents such as ethylenediaminetetraacetate, its alkali metal salts, for example tetrasodium salt, ethylenediamine or phenanthroline. At this time, the reduction (or actual copperization) is generally effected using a reducing agent capable of depositing copper (0) from a copper salt solution such as formaldehyde or sodium formate.

From the observations so far, the inventors believe that electroless deposition produces particularly small copper particles. Their size is generally less than 50 nm, preferably less than 20 nm, as measured by X-ray diffraction.

Regardless of the manner in which copper is applied to the carrier, the resulting powder or corresponding shaped article is calcined in air or at a temperature of 250 to 450 ° C. for 1 to 24 hours in an inert gas atmosphere, advantageously a nitrogen atmosphere. The molded article may be molded before or after calcination.

The catalyst powders obtained from electroless deposition or from the other methods described above are preferably molded articles, for example tablets, strands, cyclics, wheels, stars, monoliths, spheres, granules, usually by mixtures of tableting aids. It is compressed into a shaped article, preferably a tablet, such as a mold or an extrusion. Conventional tableting aids can be used, for example graphite, magnesium, stearate, methylcellulose (eg Walocel®), copper powder, or mixtures thereof.

The copper content of the catalyst is usually from 0.01 to 50% by weight, preferably from 2 to 30% by weight, particularly preferably from 5 to 20% by weight, based on the total amount of catalyst material.

The BET surface area (measured according to DIN 66131) of the catalyst is generally at least 30 m 2 / g, preferably 50 to 300 m 2 / g, particularly preferably 100 to 250 m 2 / g.

Dehydrogenation of cyclohexanol to cyclohexanone is generally carried out in the gas phase at 180 to 400 ° C, preferably at 200 to 350 ° C, particularly preferably at 220 to 260 ° C. The pressure is generally between 50 kPa and 5 MPa, in particular atmospheric pressure applied.

The starting material for the reaction will generally be a mixture of cyclohexanol and cyclohexanone. It is of course also possible to use pure cyclohexanol. The mixture used is usually 50 to 100% by weight of cyclohexanol, preferably 60 to 99% by weight, in particular 96% by weight, and 50 to 0% by weight of cyclohexanone, preferably 40 to 1% by weight, in particular 4 Will comprise weight percent. Cyclohexanone and cyclohexanol are typically obtained by concentrating cyclohexanol by oxidation of cyclohexane followed by distillation of cyclohexanone and other low boiling materials.

Generally, the catalyst is reduced using hydrogen before the actual reaction. This is generally carried out by passing a hydrogen stream diluted with an inert gas, preferably nitrogen, at a specific temperature, preferably from 120 to 300 ° C., over the catalyst. At this time, the hydrogen content of the reducing gas is typically increased continuously until no further significant changes occur at this temperature.

In a preferred embodiment, the starting material is passed through the catalyst phase as gas at a liquid space velocity per hour (LHSV) of 0.1 to 100 h ⁻¹ , particularly preferably 0.1 to 20 h ⁻¹ . The starting material may be mixed with an inert gas such as nitrogen or with water vapor. The dehydrogenation product can be finished in a conventional manner for further processing (see, for example, DE-A 1,296,625 and 1,443,462).

In another preferred embodiment, hydrogen is added to the gas mixture which is separated from the reaction mixture leaving the reaction zone and introduced into the reaction zone. It is more advantageous to recycle the reaction mixture until the desired conversion is achieved.

The catalyst of the present invention is so active that it can be operated at temperatures much lower than the reaction temperatures of currently used catalysts, which are activated quickly to provide high selectivity and conversion rates close to equilibrium. In addition, significant inactivation occurs only after a clearly longer period of time than conventionally existing catalysts.

The catalyst of the present invention is notable for its good refining capacity, adequate hardness, high conversion at low operating temperatures, high cyclohexanone selectivity and long operating life.

<Example 1>

Catalyst manufacturing

5 g of polyvinylpyrrolidone ("PVP", manufactured by Merck, Order No. 7443, average molar amount 25,000 g / mol) was calculated as 27.27 g of 11 wt% Pd (NO ₃ ) ₂ solution (Pd To a mixture of 495 ml bidistilled and 495 ml ethanol and the resulting mixture was refluxed for 4 hours. The palladium content of the resulting sol (“Pd sol”) was 0.34% by weight (based on the total amount of Pd sol).

20.6 mL of the above prepared Pd sol was mixed with 23 mL of water and 125 g of α-Al ₂ O ₃ (manufactured by Alcoa, BET surface area of 156 m 2 / g, water absorption: 0.35 mL per 1 g of Al ₂ O ₃ ). The saturated carrier was then naturally dried. The pretreated and dried carrier was suspended in 38989 ml of freshly prepared solution in which 0.1 M of Cu (OAc) ₂ , 0.2 M Na ₄ EDTA, 0.2 M formaldehyde and 0.0125 M pyridine were present. The pH was set to 12.5 with 35 wt.% NaOH and stirred vigorously. A change from dark gray to reddish brown was observed. The suspension was heated to 70 ° C. and the pH was maintained between 12 and 12.5 with additional NaOH (NaOH consumption: about 400 mL). The suspension was stirred at 70 ° C. for 30 minutes and then cooled to room temperature. The suspension was filtered to wash the filter residue neutrally (filtrate was light blue). The washed solids were then dried at 110 ° C. under nitrogen atmosphere for 16 hours and then calcined at 300 ° C. for 2 hours.

The resulting catalyst contained 16.5 wt% copper and 0.046 wt% sodium based on the total amount of dark gray catalyst.

The crystalline constituents were measured by XRD to obtain data of Al ₂ O ₃ (19 nm), CuO (13.0 nm), Cu ₂ O (trace).

<Formation of tablets (length 5 mm, diameter 3 mm)>

100 g of the catalyst powder prepared above was pre-compressed with 1 wt% of copper powder “FFL” (Norddeutsche Affinerie # 10914) and 1 wt% of magnesium stearate (Riedel de Haen # 4162757) based on the weight of the catalyst, respectively, 20 mm in length. And tablets with a diameter of 1 mm were molded. These tablets were then passed through a sieve of mesh size 1.6 mm, then 2% by weight of graphite was added and compression molded into tablets 5 mm in length and 3 mm in diameter.

The side grinding strength of the tablets was 53 N, with a standard deviation of 16 N (measured using an instrument from Frank, model No. 81557).

<Example 2>

Catalyst test

The catalyst test was carried out in a tubular reactor 5 cm in diameter and 60 cm in length. For each test, 200 ml of catalyst was charged and activated with hydrogen prior to the reaction. Prior to introducing the starting material, the catalyst was activated at 120 ° C. with 150 L of N ₂ per hour and 1.5 L of H ₂ per hour. The hydrogen stream was stopped as soon as the temperature had risen above 10 ° C. Subsequently, the hydrogen supply rate was kept constant while the temperature was raised to 240 ° C by 20 ° C. The catalyst was then activated at 240 ° C. with 150 L of N ₂ per hour and 7.5 L of H ₂ per hour. After activation, the catalyst was exposed to a 96% cyclohexanol / 4% cyclohexanone mixture at about 0.7 h ^-1 LHSV. Reactor effluent was analyzed by gas chromatography. The results are shown in Table 1 below.

Comparative Example

The dehydrogenation test of Example 2 was repeated using a commercial copper catalyst (catalyst CU 940 from Procatalyse).

catalyst Temperature (℃) Time (h) % Conversion Selectivity (%) Example 2 229 42 57 97.7 228 150 56 99.2 228 246 59 99.4 226 438 55 99.9 229 558 55 99.7 237 630 61 99.6 242 774 60 99.5 Comparative example 277 0 68 98.3 275 12 63 98.4 275 24 62 98.5 275 36 61 98.6 276 48 61 98.5 280 168 60 98.1

The catalyst of the present invention provided a conversion close to equilibrium with a very high selectivity of> 99% at temperatures as low as> 230 ° C. Significant deactivation of the catalyst did not occur at this temperature. The conversion could be increased to about 60% by slightly raising the reaction temperature to about 240 ° C. without loss of selectivity. At this temperature, deactivation also occurred very gradually.

As can be seen from this, in the comparative test, after only 168 hours of temperature adjustment was required to maintain the conversion, this correction was not required even after about 600 hours when using the catalyst prepared according to the present invention. . In addition, the temperature of the comparative example was about 40 ° C. higher than the temperature of the representative example. As a result, the selectivity of the representative examples was optimal. This could not be predicted for alumina with a BET surface area of greater than 30 m 2 / g.

Claims (6)

Α-alumina phase copper catalyst with a BET surface area (measured according to DIN 66131) of at least 30 m 2 / g. 30 m 2 / g BET surface area (as measured according to DIN 66131), which can be obtained by applying copper to α-alumina carrier material by impregnation, precipitation, dry mixing or electroless coppering in a conventional manner Α-alumina copper catalyst described above. Copper is applied to a BET surface area (measured according to DIN 66131) of at least 30 m 2 / g of α-alumina carrier material by impregnation, precipitation, dry mixing or electroless copperation in a customary manner, according to claim 1. Method for preparing a catalyst. 4. The process according to claim 3, further comprising processing the catalyst into shaped articles, in particular tablets, strands, rings or cylinders. Use of the catalyst according to claim 1 or 2 or the catalyst prepared by the method of claim 3 for producing cyclohexanone by dehydrogenation of cyclohexanol. Use of α-alumina of at least 30 m 2 / g of BET surface area (measured according to DIN 66131) for preparing the catalyst.